Centrifugal pump stage, centrifugal pump and use of a pump stage

ABSTRACT

The pump stage for a centrifugal pump comprises an impeller unit ( 10 ) having an axial hub and a diffuser unit ( 20 ) extended at a first face of said impeller unit ( 10 ). The impeller unit ( 10 ) is supported floating inside the diffuser unit ( 20 ). A shim ring ( 40 ) is associated with the impeller unit ( 10 ) and is sustained in sliding support on a washer ( 27 ) housed in a fixed position in a correspondent seat ( 26 ) of the diffuser unit ( 20 ) of an adjacent pump stage.

TECHNICAL FIELD

The present invention concerns a pump stage to be used in a centrifugal pump, in particular of submerged type.

BACKGROUND ART

It has been known that for transferring a liquid from a lower space to a higher space, pump members are generally used, such as in particular submerged pumps. Known submerged pumps generally have an external tubular sleeve provided with a plurality of radial openings for the entrance of the fluid, usually called aspiration openings, and with an opening for the exit of the liquid, called outlet opening. The operative members of the pump are housed inside the sleeve. The operative members are made up of a pump unit and a motor unit, generally of electric type, suitable to operate the transferring of the liquid from the aspiration openings to the outlet opening.

The pump unit is usually made by one or more stages, each comprising a rotating member, suitable to be driven in rotation by the motor shaft of the motor unit, and by stationary members suitable to convey the liquid from a stage to another, until the outlet opening.

Patent U.S. Pat. No. 7,290,984 discloses for example a centrifugal pump having more stages, in which each stage comprises an impeller unit, a stationary disc unit and a diffuser unit, arranged about the motor shaft or impeller shaft. More specifically, the disc unit is arranged adjacent to a first side of the impeller unit; the diffuser unit is arranged adjacent to a second side of the impeller unit. The hub of the impeller is provided with floating seal means, supported by the diffuser unit, suitable to reduce the re-circulation of the liquid. A thrust washer, arranged about the motor shaft, is suitable to engage the hub of the impeller and the cited seal means of the hub of the impeller. A sliding coupling ring, fixed to the stationary disc unit, engages a correspondent surface of the impeller.

In substance, the seal means of the hub are made up of a circular disc-shaped flange having a series of radial protrusions to couple with correspondent seats shaped on the body of the diffuser, about the passage opening of the shaft. The flange encloses a cup shaped hub portion provided with a circular opening in the transversal part.

A specific problem complained by users of pumps of known type is the progressive wear and tear of the mobile parts being in reciprocal contact, at which the seal is carried out. In particular, the impeller is usually sustained in sliding support, at an annular portion thereof, on the disc facing it. The axial thrust which acts on the impeller acts as well on the disc and, due to the shim effect produced by the functioning, this causes a progressive wear and tear of the parts. This fact obviously limits the pump life, especially in presence of grains of sand in the pump liquid.

Patent U.S. Pat. No. 3,265,001 describes a multi-stage centrifugal pump in which the impeller of each stage is supported floating at the relative diffuser unit. The impeller hub is in fact mounted axially slidable on the motor shaft by which it is driven in rotation; the stroke of the floating impeller is limited by suitable stop means, for example of annular shape, mounted on the motor shaft. The impeller is supported in sliding contact, along an annular portion, at the cited lid of the diffuser unit, to make up a seal zone between the rotating part and the static part of the stage. More in particular, the impeller is supported by means of a thrust bearing placed beneath the hub of the same impeller, in support on a seat of the underlying diffuser.

Such solution allows to reduce the wear and tear of the working members, in particular in case the sand or other abrasive grains are present in the liquid to be pumped. The impeller being mounted floating thus allows to prevent abrasive grains to stop at the sliding contact seal zones, thus preventing that such particles increase the wear and tear phenomena.

At the same time, it is necessary to limit as long as it is possible the phenomena of leaking of the liquid from the rotating to the static part of each stage of the centrifugal pump, in order to prevent a decrease of the pump performances. For this reason, a sufficient seal between the rotating part and the static part of each stage of the centrifugal pump must be ensured.

Solutions known in the specific field do not fully satisfy the above mentioned exigencies.

DISCLOSURE

The task of the present invention is that of solving the aforementioned problems, by devising a pump stage which ensures a high-level performance as well as long endurance in any functioning condition.

Within such task, it is a further scope of the present invention that of providing a pump stage with reduced wear and tear of the mobile parts in contact with one another, to give the pump a longer life.

Another scope of the present invention is that of providing a pump stage which eases the assembly of the pump unit.

A further scope of the invention is that of providing a pump stage having a simple practical and functional conception, provided with a surely reliable functioning, versatile use as well as relative economic cost.

The cites scopes are attained, according to the present invention, by the pump stage according to claim 1.

According to the present invention, the pump stage comprises an impeller unit which is supported floating inside a relative diffuser unit through a shim ring mounted fixed on an axial hub of the impeller unit and sustained in sliding support on a washer housed in fixed position in a correspondent seat of the diffuser unit of an adjacent pump stage.

The impeller unit is in sliding contact, along an annular portion extended at said second face, with an aspiration lid associated with said diffuser unit.

According to an advantageous aspect of the invention, in a starting or breaking instep, between said annular portion of the impeller unit and said lid, a little play is defined, such as to minimize the hydraulic losses by drawing without contact.

Preferably, said play is equal to a few decimillimetres.

Advantageously, at the end of the said starting or breaking in step, the impeller unit is in support with said shim ring on said washer of the diffuser unit of the adjacent pump stage and with said annular portion on sad lid.

In such way, the hydraulic thrust acting on the impeller unit is distributed on two support surfaces, that is the lid on which the impeller annular portion is in support and the adjacent pump stage washer on which the shim ring is in support.

Preferably, the shim ring is protruding for a part from the axial hub of the impeller unit and it axially crosses said lid of the diffuser unit for engaging in sliding support said washer of the diffuser unit of the adjacent pump stage.

Preferably, said washer is housed in a seat made at a circular opening axially made up by said diffuser unit.

Preferably, the shim ring is made of a low friction coefficient material and is sustained in sliding support on a washer of metallic material.

Preferably, the shim ring is made of plastic material, for example a polymer having a low friction coefficient and high endurance without requiring lubrication.

Preferably, said washer is housed in a seat made at a circular opening axially made up by said diffuser unit.

Preferably, the lid comprises a disc of metallic material or partially metallic, centrally having a circular opening with raised rim on which said annular portion of said impeller unit is in sliding contact.

The invention also concerns a centrifugal pump comprising a pump unit made up of a plurality of pump stages, as previously described.

It is an object of the invention also the use of a centrifugal pump stage which provides a starting or breaking in phase in which said impeller unit is arranged in support with said shim ring on said washer of the diffuser unit of the adjacent pump stage and in which between said annular portion of the impeller unit and said lid a clearance is defined. The width of said clearance progressively reduces because of the wear and tear of said shim ring, until annulling in a normal working condition or speed, in which said annular portion of the impeller unit is in support on said lid.

The breaking in of the pump determines a slight wear and tear of the shim ring which in this way is polished and thus acquires a high endurance.

DESCRIPTION OF DRAWINGS

Details of the invention shall be more apparent from the detailed description of a preferred embodiment of the pump stage according to the invention, illustrated for indicative purposes in the attached drawings, wherein:

FIG. 1 shows an axial cross-section view of the pump stage according to the invention;

FIG. 2 shows a perspective exploded view of the same pump stage;

FIG. 3 shows an axial cross-section view of a couple of pump stages in assembly position.

BEST MODE

With particular reference to such figures, the pump stage, to be used in a centrifugal pump, in particular of submerged type, known per se and therefore not represented in the drawings, has been indicated for more clarity in its entirety with 1.

The pump stage 1 comprises an impeller unit 10 having an axial hub 11, to be associated with a motor shaft of the electric pump, not represented. The impeller 10 is mounted floating inside a correspondent diffuser unit 20, to which an aspiration lid 30 is made integral. The diffuser unit 20 extends at a first face of the impeller unit 10; the lid 30 extends at an opposed second face of the impeller unit. In vertical working position, the first face of the impeller unit 10 is arranged on the top, substantially horizontal, while the second face is arranged inferiorly.

More in particular, the impeller unit 10 is made up of an upper part 12 which extends transversally from the axial hub 11 and a lower part 13 substantially disc shaped. The parts 12, 13 of the impeller unit 10 are preferably made of a plastic material being very rigid and durable, of the type for example of poliossimetilene and the like. The upper part 12 shapes the above mentioned first face of the impeller unit 10; the lower part 13 shapes the above mentioned second face of the impeller unit 10. The upper part 12 of the impeller unit 10 shapes, in angularly distributed positions, a series of walls 14 which extend in spiral shape from the central zone towards the peripheral zone of the impeller unit 10. The walls 14 make up, in cooperation with the lower part 13 of the impeller unit 10, respective flow channels 15 for the liquid to be pumped.

The diffuser unit 20 has an external cylindrical body 21, preferably made of plastic rigid material, for example a reinforced thermoplastic material. A profiled plate 22 centrally having a circular opening 23 extends from the top of the cylindrical body 21 towards the inside. Above the plate 22, a series of keys 24 are shaped in angularly distributed positions, and extend in spiral from the central zone towards the peripheral zone of the diffuser unit 20. The keys 24 shape respective flow channels 25 for the liquid to be pumped.

The plate 22 shapes, at the opening 23, a seat 26 for housing a washer 27 preferably of metallic material, for example stainless steel. The washer 27 has an inner diameter smaller than the diameter of the opening 23.

The aspiration lid 30 has the shape of a disc centrally having a circular opening 31; the disc 30 is preferably made of metallic or partially metallic material, for example stainless steel. At the opening 31, the disc 30 has a zone curved outwardly suitable to shape a rim 32 raised with respect to the plane of the same disc 30. The disc 30 peripherally engages a correspondent shoulder made along the lower edge of the cylindrical body 21 of the diffuser unit 20.

A shim ring 40 is inferiorly associated with the axial hub 11 of the impeller unit 10, suitable to engage, in assembly configuration, the upper face of the washer 27 with thrust bearing functions. The shim ring 40 is fixed to the hub 11. More specifically, the shim ring 40 is inserted in a portion of reduced diameter 16 of the hub 11, to result protruding for a part from the same hub 11. The shim ring 40 is preferably made of plastic material, for example a low friction polymer with great endurance and not requiring lubrication, of the type of polyether-ether-ketone (PEEK).

The functioning of the pump stage is easy to understand from the preceding description.

In assembly configuration inside the tubular body of the pump, the single pump stages shaping the pump unit are coupled to one another through the insertion in series on the motor member. More in particular, the external cylindrical body 21 of the diffuser unit 20 is inserted at the base of the cylindrical body 21 of the underlying diffuser unit (see FIG. 3). In such configuration, the disc 30, which inferiorly closes the diffuser unit 20, results to be locked against the cylindrical body 21 of the underlying diffuser unit.

The impeller unit 10, arranged inside the vane shaped between the diffuser unit 20 and the disc 30 of the pump stage, is in support through the shim ring 40 on the washer 27 housed in the corresponding seat 26 of the underlying diffuser unit. In practice, in assembly configuration the impeller unit 10 of the pump stage is sustained in sliding support on the washer 27 of the diffuser unit 20 of the underlying pump stage.

Moreover, the lower part 13 of the impeller unit 10 is in sliding contact along an annular portion 13 a, substantially internal, with the raised rim 32 of the disc 30 inferiorly closing the diffuser unit 20.

In practice, in use, the impeller unit 10 is supported floating at the relative diffuser unit 20 of the pump stage through the shim ring 40 of low friction plastic material, fixed to the hub 11 and sustained in sliding support on the metal washer 27 fixed in rigid manner on the diffuser unit of the underlying pump stage; the impeller unit is in sliding contact, along an inner annular portion 13 a of the inferior disc 13, with the rim 32 of the lid 30 of metallic material of the diffuser unit.

More in particular, during the first activation of the pump, substantially of breaking in, the hydraulic thrust acting on the impeller unit 10 is borne by the shim ring 40 sustained in sliding support on the metal washer 27; while between the annular portion 13 a of the lower disc 13 of the impeller and the rim 32 of the lid 30 there is a clearance, that is a little play, for example equal to a few decimillimetres, so that the hydraulic losses by leak are minimized, even without there being a contact.

The breaking in of the pump determines the occurrence of a slight wear and tear on the shim ring 40, which in this way is polished and consequently acquires a high resistance to wear and tear. The wear out of the shim ring 40 progressively reduces the play between the annular portion 13 a of the lower disc 13 of the impeller and the rim 32 of the lid 30, until the lower disc 13 is brought in contact with the rim 32 of the lid 30. In this way, the hydraulic losses by leak are almost completely eliminated between the two seal surfaces, thus improving flow rate and hydraulic head performances.

Moreover, in this way the hydraulic thrust which acts on the impeller unit 10 is distributed on the lid 30 of the diffuser unit 20, thus reducing the wear and tear of the mobile parts in contact. This causes the extension of the life of the pump also in presence of grains of sand in the pumped liquid.

It is to be observed that even in case of incorrect assembly, possibly due to physical imperfections, in case the contact between the lower disc 13 of the impeller and the rim 32 of the lid 30 does not occur before the contact between the shim ring 40 and the metal washer 27, the wear and tear of the upper shim would produce the progressive lowering of the shim ring 40 on the washer 27, balancing again the axial thrust.

The pump stage according to the present invention attains therefore the scope of ensuring a high performance level in any functioning condition, as well as of easing the assembly of the pump unit.

Such result is essentially obtained thanks to the inventive idea of making the impellers 10 of the different pump stages floating with respect to the relative diffusers 20 so as to split the axial thrusts on two support surfaces, the lid 30 which supports the annular portion 13 a of the impeller and the washer 27 of the adjacent pump stage which supports the shim ring 40, thus optimizing the shim play in the course of time.

Moreover, this makes easier the assembly of the different pump stages.

Such solution allows as well to obtain a wider tolerance with respect to the concentricity of the different components, with the advantage of being able to provide more pump stages.

Finally, the pump stage according to the present invention allows to improve the pump performances, that is to provide less pump stages while generating the same flow rate.

It is to be observed that the materials used for the sliding couplings between the impeller 10 and the disc 30 and between the shim ring 40 and the washer 27 allow to minimize the friction effects, while ensuring an efficient seal from liquid passage. Such materials are suitably chosen, also taking into account the possible presence of grains of sand and the like in the liquid.

A further advantage offered by the pump stage according to the invention, is due to the considerable simplification of the inner seal system and thus to the reduced costs which it entails, also in terms of assembly.

The pump stage described for indicative purpose is susceptible of numerous modifications and variants according to the different exigencies.

In practice, the embodiment of the invention, the materials used, as well as the shape and dimensions, may vary depending on the requirements.

Should the technical characteristics mentioned in each claim be followed by reference signs, such reference signs were included strictly with the aim of enhancing the understanding the claims and hence they shall not be deemed restrictive in any manner whatsoever on the scope of each element identified for exemplifying purposes by such reference signs. 

1. A pump stage for a centrifugal pump, comprising: an impeller unit comprising an axial hub suitable to be mounted on a pump shaft of the centrifugal pump coaxial with the pump shaft; a diffuser unit extending at a first face of said impeller unit; an aspiration lid associated with said diffuser unit and extended at a second face of said impeller unit, said impeller unit floating inside said diffuser unit, said impeller unit being associated with a shim ring mounted fixed on said axial hub and sustained in sliding support on a washer housed in a fixed position in a correspondent seat of the diffuser unit of an adjacent pump stage, said impeller unit being in sliding contact with said aspiration lid, along an annular portion extended at said second face.
 2. A pump stage according to claim 1, wherein, in a starting or breaking in step, between said annular portion of said impeller unit and said aspiration lid a little play is shaped, such as to minimize hydraulic losses by leak without there being a contact.
 3. A pump stage according to claim 1, herein a portion of said shim ring protrudes from said axial hub of the impeller unit and axially crosses said aspiration lid of the impeller unit for engaging in sliding support said washer of the diffuser unit of the adjacent pump stage.
 4. A pump stage according to claim 2, wherein, at an end of said starting or breaking in step, said impeller unit is in support with said shim ring on said washer of the diffuser unit of the adjacent pump stage and with said annular portion on said aspiration lid.
 5. A pump stage according to claim 1, wherein said shim ring is made of low friction coefficient and high resistance to wear and tear material and is sustained in sliding support on said washer of metallic material.
 6. A pump stage according to claim 1, wherein said washer is housed in said seat made at a circular opening axially made up by said diffuser unit.
 7. A pump stage according to claim 1, wherein said aspiration lid comprises a disc of metallic or partially metallic material centrally having a circular opening with a raised rim on which said annular portion of said impeller unit is in sliding contact.
 8. A centrifugal pump comprising: a pump comprising a plurality of pump stages, one or more of said pump stages comprising an impeller unit comprising an axial hub suitable to be mounted on a pump shaft of the centrifugal pump coaxial with the pump shaft, a diffuser unit extending at a first face of said impeller unit and an aspiration lid associated with said diffuser unit and extended at a second face of said impeller unit, said impeller unit floating inside said diffuser unit, said impeller unit being associated with a shim ring mounted fixed on said axial hub and sustained in sliding support on a washer housed in a fixed position in a correspondent seat of the diffuser unit of an adjacent pump stage, said impeller unit being in sliding contact with said aspiration lid, along an annular portion extended at said second face.
 9. A method, comprising: using a centrifugal pump stage, said centrifugal pump stage comprising an impeller unit comprising an axial hub suitable to be mounted on a pump shaft of the centrifugal pump coaxial with the pump shaft, a diffuser unit extending at a first face of said impeller unit and an aspiration lid associated with said diffuser unit and extended at a second face of said impeller unit, said impeller unit floating inside said diffuser unit, said impeller unit being associated with a shim ring mounted fixed on said axial hub and sustained in sliding support on a washer housed in a fixed position in a correspondent seat of the diffuser unit of an adjacent pump stage, said impeller unit being in sliding contact with said aspiration lid, along an annular portion extended at said second face; providing a starting or breaking in stage in which said impeller unit is arranged in support with said shim rig on said washer of the diffuser unit of the adjacent pump stage and a clearance is shaped between said annular portion of said impeller unit and said aspiration lid, a width of said clearance undergoing to a progressive reduction by wear out effect of said shim ring, until annulling in a condition of normal functioning or speed, in which said annular portion of said impeller unit is in support on said aspiration lid.
 10. A method according to claim 9, wherein said wear and tear effect, in said starting or breaking in step, said shim ring is polished and consequently acquires a high endurance.
 11. A pump stage according to claim 2, wherein a portion of said shim ring protrudes from said axial hub of the impeller unit and axially crosses said aspiration lid of the impeller unit for engaging in sliding support said washer of the diffuser unit of the adjacent pump stage.
 12. A pump stage according to claim 3, wherein, at an end of a starting or breaking in step, said impeller unit being in support with said shim ring on said washer of the diffuser unit of the adjacent pump stage and with said annular portion on said aspiration lid. 